CONICET | Buscador de Institutos y Recursos Humanos

Different cut-off values, from 3 to10 ng/ml, depending on the assays, have been defined for pharmacological test (PhT) of growth hormone (GH) secretion, based on biochemical and clinical studies. Recently, a 22K recombinant GH isoform IRP IS 98/574 have been commercialized. We had previously defined a 6.1 ng/ml value, in terms of ICMA IRP IS 80/505 as serum GH cut-off limit in PhT of GH secretion. Objective and hypotheses: Our aim was to assess which is the GH deficiency (GHD) diagnostic cut-off limit of serum GH in PhT of GH secretion for ICMA immunoassay with the IRP IS 98/574. Methods: We analyzed serum GH concentration in 138 serum samples, using ICMA calibrated with both IS 80/505 and IS 98/574. Blood samples (n=138), from 92 different individuals, (103 males and 35 female; age range, 2.5 15.0 years) were used. All samples were selected from arginine and clonidine PhT. Results: We found high significant linearity (y = 0.7307x + 0.2768, p<0.001) between ICMA IS 98/574 (y) and ICMA IS 80/505 (x). The y value for fixed x value of 6.1 ng/ml in the ICMA IS 80/505 was calculated, and a diagnostic cut-off limit for ICMA IS 98/574 was estimated as 4.7 ng/ml. ICMA IS 98/574 / ICMA IS 80/505 ratio plot and 95% prediction interval was 0.79±0.17. Linearity and Bias were reconfirmed by Passing Bablock analyses and the Wilcoxon test respectively. Conclusions: High significant linearity and differences among the assay with different IS were found. To suspect the diagnosis of GHD, we propose 4.7 ng/ ml as the serum GH cut-off limit value in PhT for ICMA immunoassay with the IRP IS 98/574as. Finally for each GH assay, an appropriate cut-off value for serum GH maximum peak response to PhT should be strongly recommended .